1. Field of the Invention
The present invention relates to a cutting insert used for threading work.
2. Description of the Related Art
In a screw cutting edge of a cutting insert for pipe threading work called a chaser among cutting inserts for threading work, a plurality of tooth-shaped convex cutting edges are arranged substantially in parallel by predetermined intervals. It is general that the predetermined interval herein is defined as an interval equal to a pitch of a screw to be processed.
In the cutting insert for threading work, for preventing degradation of shape accuracy of the screw to be processed, it is general to form a ridge line and flanks of the cutting edge by grinding work using a grinding stone. In a screw cutting edge in this cutting insert for threading work, a length in a direction along the cutting edge is long, and a contour shape of the cutting edge is complicated as viewed from a rake face side. Therefore there is a problem that the time required for grinding work is long.
For overcoming the above problem, for example, a cutting insert disclosed in Japanese Patent Laid-Open No. 2007-313590 is proposed. According to this cutting insert, when the cutting insert for threading work performs threading work, at least one of the cutting edges in a front side of a relative feeding direction is defined as a roughing cutting edge, at least one of the cutting edges in a back side of the relative feeding direction is defined as a finishing cutting edge, wherein a height of a tooth of the roughing cutting edge relative to an internal reference line parallel to a relative feeding direction of the insert is lower than that of a tooth of the finishing cutting edge. In a case where the tooth shape of the roughing cutting edge and the tooth shape of the finishing cutting edge overlap, the roughing cutting edge is formed to be smaller in such a manner that the roughing cutting edge is accommodated in a footprint of the finishing cutting edge, and a surface roughness of the flank in the roughing cutting edge is rougher than that of the flank in the finishing cutting edge. This structure enables the time in the grinding process of the cutting edge to be shortened and manufacturing costs of the cutting edge to be suppressed, and further, screw cutting work to be realized with high accuracy as conventional.